20 rounds and changing zero

[Deleted member 10043]

I have one 700 that takes about 20 rounds to return to zero. Starts off as much as .3 mils lower at 200 meters and will stay there even shooting sub moa. Then out of nowhere I'm back to my original 100 yard zero and still shooting sub moa. Next month or so same thing every time. Rifle is 260, B&C M40 stock, 30" Bartlein. I'm thing scope mounting problem. Anybody else?

 

[winniethepooh]

Barrel free floated?

 

[wade2big]

What exactly do you mean? Rifle shoots to point of aim. Take it home and put it up. Next time you bring it out it’s shooting slightly high. After 20 rds, the POI works it way back down. Take it home and put it up. Repeat. Is that correct?

 

[Deleted member 10043]

Starts out with .3 mils up at 200 meters. After about 20 rounds the dope is like .6 mils up. And will stay at that +.3 mils extra for the rest of the shooting session. Next time out same thing. So, it something that repeats itself.

 

[Deleted member 10043]

If I remember right the original 100 zero called for .3 up.

 

[Rthur]

Starts out with .3 mils up at 200 meters. After about 20 rounds the dope is like .6 mils up. And will stay at that +.3 mils extra for the rest of the shooting session. Next time out same thing. So, it something that repeats itself.

Are you resetting your Elevation knob to the new zero or just dialing/holding offset?

R

 

[Deleted member 10043]

Free floated barrel, yes.

 

[Deleted member 10043]

Are you resetting your Elevation knob to the new zero or just dialing/holding offset?

R

I'm just dialing rather than resetting the knob.

 

[Longshot231]

I agree with winniethepooh. If your barrel is not free floated that could also be a problem.

My rifles will also shoot a little higher from a clean bore with oil in it. After a fouling shot or two or thee or four, it will settle back down to zero.

If I remember to do it, I will take a small bottle of acetone with me prior to varmint hunting. Then right before going to the field, I will swab the bore out with a patch soaked with acetone, to get rid of any oil. That doesn't quite replicate the conditions after a fouling shot is taken but at least the oil is removed.

I've also done that prior to checking the zero at the range. It's not quite like a fouling shot but gets the oil out. Remember that after the first shot, all the oil is blown out of the bore. With the oil in the bore, the friction is less and velocity is greater meaning that the point of impact is higher on the first shot. At least that's my theory on one factor that affects the first round shot. However, it usually doesn't take 20 rounds for my rifles to return to zero.

Another factor is how you have your rifle zeroed; on sand bags, a bipod, sitting at a bench or prone. I try to zero my rifles the way I hunt with them; on the ground, prone and on the bipods. If you change the way you are checking the zero every time you shoot, you will definitely notice a change in the point of impact. For me, I notice a big change between shooting from a bench versus shooting on the ground in the prone position with bipods.

 

[Deleted member 10043]

Went back and checked the data. Original dope for 100 zero is .5 mils. What is happening is now the dope at 200 meters works it way from cold barrel .3 up to about 20 rounds at .5 up and then stays there. There are times it can take up to 30 rounds.

 

[wade2big]

I agree with winniethepooh. If your barrel is not free floated that could also be a problem.

My rifles will also shoot a little higher from a clean bore with oil in it. After a fouling shot or two or thee or four, it will settle back down to zero.

If I remember to do it, I will take a small bottle of acetone with me prior to varmint hunting. Then right before going to the field, I will swab the bore out with a patch soaked with acetone, to get rid of any oil. That doesn't quite replicate the conditions after a fouling shot is taken but at least the oil is removed.

I've also done that prior to checking the zero at the range. It's not quite like a fouling shot but gets the oil out. Remember that after the first shot, all the oil is blown out of the bore. With the oil in the bore, the friction is less and velocity is greater meaning that the point of impact is higher on the first shot. At least that's my theory on one factor that affects the first round shot. However, it usually doesn't take 20 rounds for my rifles to return to zero.

Another factor is how you have your rifle zeroed; on sand bags, a bipod, sitting at a bench or prone. I try to zero my rifles the way I hunt with them; on the ground, prone and on the bipods. If you change the way you are checking the zero every time you shoot, you will definitely notice a change in the point of impact. For me, I notice a big change between shooting from a bench versus shooting on the ground in the prone position with bipods.

I thought bench rest shooters clean their bores more often because a fouled rifle speeds up not slows down.

I shoot every weekend and never have a problem with a wondering zero. I also don’t shoot very often for groups (almost never) so maybe I just don’t notice. The only thing I notice is cooler temperatures slowing velocity. I only see this down range though. I don’t notice a difference shooting off a bipod or off of bags. Same dope same results down range.

I hardly ever clean the the bores of my rifles after a short break in. I may do a light cleaning every 500 rds or so. Maybe this has something to do with it. Give that a try Culpeper.

 

[Deleted member 10043]

It's off the bench but it is 1.5 moa silhouetted steel at 200, 300, 385, and 500 meters. But that doesn't have anything to with the problem except makes it easier to observe repeatability. It doesn't matter if the bore is clean or not. Same thing with the problem.

 

[Rthur]

Went back and checked the data. Original dope for 100 zero is .5 mils. What is happening is now the dope at 200 meters works it way from cold barrel .3 up to about 20 rounds at .5 up and then stays there. There are times it can take up to 30 rounds.

Sounds crazy but rezero your scope and take another range trip or two.
30 rounds seems like a lot to be cold shooter but I've seen stranger things.

R

 

[Deleted member 113831]

So your barrel is heat walking by an MOA or so. Not that unusual.

It's pretty easy to test it. Shoot 20 rounds with 5 minutes between each round at 100 or 200 yards. Then shoot a 20 round string and see if there is a difference in average POI.

 

[Deleted member 10043]

I'll do that, Skook and post results. Okay, if the barrel is the culprit it should be retired. 20-30 rounds is beyond acceptable. I'm going to bore scope it and if I see anything unusual I'll snap some pics. Then I'll clean it good and check everything else top to bottom. If I find anything amiss I'll post that too.

I need this like I need a bag on my hip. I've got a couple of other rifle projects going on too.

 

[spife7980]

You don’t have a muzzle brake or something that is slowly working it’s way loose or installed on a dirty shoulder do you? If so put a wrench on it and give it a good whack tight.
When I’ve noticed my zero shift it’s usually because something hanging off the barrel isn’t tight.

 

[Deleted member 10043]

This is a naked barrel but good suggestion.

Now that I think back I had a similar problem almost to a tee on a Varmint Savage. Eventually, replaced the barrel and the problem went away.

 

[Deleted member 10043]

Okay, one step at a time. This rifle has zee rings. Each ring has four bolts. All had backed out. Torqued each set. It is possible it recoils enough to set the plastic inserts as far as it can. Then when rifle sits up for several weeks it eases back into the position of least resistance or something related to that. If this doesn't correct the problem I'll post the next step. Also, going to clean bore and take a look see inside. If I find anything remarkable I'll post it up.

 

[ranger3]

I have a 260 that shoots 1k zero for 20 rounds, then adds 1.5 moa stays there until bare is cold, starts all over again
Everything is good with scope and barrel is floated. I suspect stress in the barrel when it warms up. Could be your problem. This is repeatable. I have also suspected my stock is doing something funny.

 

[Deleted member 113831]

Okay, one step at a time. This rifle has zee rings. Each ring has four bolts. All had backed out. Torqued each set. It is possible it recoils enough to set the plastic inserts as far as it can. Then when rifle sits up for several weeks it eases back into the position of least resistance or something related to that. If this doesn't correct the problem I'll post the next step. Also, going to clean bore and take a look see inside. If I find anything remarkable I'll post it up.

It is improbable that this ring issue, if it exists, would be consistent enough to be repeatable, but stranger things have happened.

 

[Deleted member 10043]

Skook, I agree with you but there enough tension to keep the scope in place and still be able to visible see the scope manipulate the inserts just by grabbing the scope and forcing it. I'm just hoping this is the problem. Probably more like @ranger3 is what is going on. I'm the only person I know that still use zee rings. There may be others but I never see them mentioned.

 

[Deleted member 10043]

Bore scope is a pass. Nothing remarkable there.

 

[Rust]

Twenty rounds in say twenty minutes will get a barrel good and hot. If I understand correctly the rifle is consistent in this shift of POI versus POA. This indicates to me at least that it is the barrel. Insufficient or no stress relief during manufacture of a barrel can result in a barrel that alters just a bit as it gets hot. A really good aftermarket barrel is stress relieved at least once during manufacture to prevent just such an occurrence.

 

[wade2big]

Twenty rounds in say twenty minutes will get a barrel good and hot. If I understand correctly the rifle is consistent in this shift of POI versus POA. This indicates to me at least that it is the barrel. Insufficient or no stress relief during manufacture of a barrel can result in a barrel that alters just a bit as it gets hot. A really good aftermarket barrel is stress relieved at least once during manufacture to prevent just such an occurrence.

He is shooting through a bartlein barrel. Could the good makers skip this process?

 

[Kickin45]

All barrels shoot differently when ice cold as opposed to hot to the touch. I have Bartlein barrels on all my bolt guns and I have 2 zeros. Cold and warmed up. I mainly bench shoot so I usually run 5 or 6 rounds of cheap ammo through the gun to warm it up. My warm zero is dead on at that point every time.
If your a hunter, you’ll need to keep the cold zero, which means firing a shot at the range and then walking away for quite awhile as the barrels cools back to cold.

 

[Kickin45]

Think of it as a car. Cars run differently cold then they do warmed up.

 

[Deleted member 10043]

In this case we are able to do the same thing with this rifle to determine repeatability of the problem. Rules are NRA Silhouette. 200, 300, 385, 500 meters 1.5 MOA square free standing targets. 10 targets per bay.

7:00 AM check zero on rifle. Should be 100 yards but at 200 meters the dope is .3 mils rather than .5 mils. This can take up to 10 rounds to figure out shooting a 2 MOA swinger at 200 meters. After getting that .3 dope at 200 meters I practice out to the other three lines. Rifle is shooting fine for the subsequent dope at 300, 385, and 500 meters. Another 10 rounds.

8:30 AM match starts. A relay is 5 shots within 2.5 minutes on the first five in the bay. Another 2.5 minutes for the remaining five. Zero has changed. I’m shooting .5 mils (100 yard zero) at 200 meters and so forth. It will remain like this the rest of the match. There are two relays so the entire match will be completed by 11:00 or so. So, a total of 40 rounds for the match over this course of time. So there is plenty of time for the barrel to heat up and cool down.

Rifle sits up for a month and I repeat the same thing as above for the next match.

 

[wade2big]

In this case we are able to do the same thing with this rifle to determine repeatability of the problem. Rules are NRA Silhouette. 200, 300, 385, 500 meters 1.5 MOA square free standing targets. 10 targets per bay.

7:00 AM check zero on rifle. Should be 100 yards but at 200 meters the dope is .3 mils rather than .5 mils. This can take up to 10 rounds to figure out shooting a 2 MOA swinger at 200 meters. After getting that .3 dope at 200 meters I practice out to the other three lines. Rifle is shooting fine for the subsequent dope at 300, 385, and 500 meters. Another 10 rounds.

8:30 AM match starts. A relay is 5 shots within 2.5 minutes on the first five in the bay. Another 2.5 minutes for the remaining five. Zero has changed. I’m shooting .5 mils (100 yard zero) at 200 meters and so forth. It will remain like this the rest of the match. There are two relays so the entire match will be completed by 11:00 or so. So, a total of 40 rounds for the match over this course of time. So there is plenty of time for the barrel to heat up and cool down.

Rifle sits up for a month and I repeat the same thing as above for the next match.

.5 mils come up from 100yds afor 200 meters (220 yards sounds about right with a .260 and an30” barrel. Your initial .3 come up seems incorrect even with your 30” barrel.

Being so repeatable i couldnt see it being anything other than the barrel but none of it makes sense to me.

 

[Deleted member 10043]

Nothing is ever easy with this stuff.

 

[FromMyColdDeadHand]

By your last post Culpepper, you never clean the rifle?

 

[Deleted member 10043]

I clean up every 100 rounds

 

[wade2big]

Will it do the same thing between cleanings? I dont have experience cleaning nearly that often. Maybe 5-600 rds or so for me and all I do is push a wet patch through, a few brush strokes, a wet patch and a couple of dry patches.

 

[steve123]

Another thing to check is if the barrel has loosened. I've had a barrel extension come loose on a AR and a barrel come loose on my bolt rifle. Both started out with small POI shifts but they got worse over time. I cracked the AR barrel extension loose with my bare hands and the bolt rifle had maybe 5-10 ftlbs of torque on it. There were reasons both loosened up which I won't go into now.

 

[Deleted member 10043]

It does the same thing clean or dirty. It is frustrating. Like dealing with this problem I shot well enough to get bumped up to Master Class. Something I've been sandbagging for years, lol.

 

[Cayjotiethumper]

What about the temperature you keep the rounds. For example they ride in the a.c. going to the range and when you get there they sit in the hot sun?

 

[Deleted member 10043]

No, I keep the ammo out of the sun.

 

[308220]

Fuck all that bullshit. Replace the barrel. The money spent on a new barrel is far more valuable than the time and frustration youll spend on that barrel.

 

[Deleted member 10043]

I had a similar moment of clarity. The fucking barrel just screws off, lol.

 

[NineHotel]

I had a barrel from a now defunct supplier that would change 1 1/4 MOA in elevation and 1/2 MOA in windage between cold shot 1 and shot 5, repeatedly. When my smith handed me back the barreled action after barreling it up, he said, I don't know where you got this barrel, but don't ever get another one. After 6 months of wrangling I got a portion of my money back, put a Krieger on it, and it holds zero cold to hot. Just like the rest of my good rifles.

 

[Rust]

He is shooting through a bartlein barrel. Could the good makers skip this process?

Repeatable POI shift as the barrel heats, with scope mounts, action bedding and the like eliminated, barrel. Not every barrel from every barrel maker is perfect even if they have an admirable track record. A 20 round string gets a barrel good and hot, a 30 round string and the barrel is probably smoking. My money is on the barrel.

 

[Deleted member 10043]

Yep.

 

[Barney88PDC]

I had a rifle that would shoot a cold round high and left then stack the rest. Came home and did my first bed job with some help and instructions over the phone before I started and after that every round went dead center. Is stress free bed it from the tang to the recoil lug. I dont like anything forward of the lug.